162 ME. J. B. scRivENOR ON [June 1912, 



has been brought b}' the younger granite mass. The older ore 

 may be readily distinguished from the younger ore by the fact 

 that the latter occurs as unworn crystals of cassiterite. 



The more I see of the Gopeng Beds in the splendid sections 

 afforded by the hydraulic and other mines, the more secure do I 

 feel in my opinion that these beds are of glacial origin. I cannot 

 expect others, however, who cannot possibly visit the locality, to 

 feel the same confidence, more especially since clear photographs 

 are difficult to obtain on account of the uniform, and generally 

 pale-grey, colouring of the sections, and on account of the fact 

 that (except in a few cases) the smaller boulders are so weathered 

 as to fracture as though they were part of the clay when a bank 

 falls in the course of mining, with the result that it is uncommon 

 to find them standing out in relief. That I am not entirely un- 

 supported, however, will be seen from a letter to the 'Mining 

 Journal ' of July 1st, 1911, in which Mr. F. E. Mair says that my 

 arguments in favour of a glacial origin are convincing. Another 

 mining engineer, who was once assistant Manager on the Kinta 

 Tin-Mines, has remarked to me on the resemblance of some sections 

 to the drift sections on the ISTorfolk coast. 



The absence of any striations on the boulders will appear 

 remarkable to those who do not appreciate the extraordinary 

 power of weathering in a humid, tropical climate ; but no one who 

 has seen how the hardest siliceous rocks can be reduced to a 

 friable state, simply by the removal of silica in solution, could 

 expect to find the surface of the boulders fresh enough to retain 

 such markings. 



In Chamberlin & Salisbury's ' Geology : Earth History ' vol. iii 

 (1906) there are some illustrations of drift to which sections that 

 I have seen at the Gopeng mines bear a striking resemblance. 

 Thus on p. 338 is a photograph of stratified drift that might have 

 been taken on the Gopeng Mining Company's land. On p. 378, 

 again, is shown a section of stratified and unstratified drift that 

 might serve for parts of the Gopeng Beds, if the boulders did not 

 stand out so prominently. 



The climatic evidence afforded by the Gopeng Beds is very 

 valuable, in that it gives so sure a basis of correlation. In the 

 words of the authors of the ' Manual of the Geology of India ' 

 (2nd ed. 1893, p. 206), 



' it is consequently justifiable to use these glacial deposits for the purpose of 

 correlation, and to conclude that the boulder-beds of the three continents were 

 formed contemporaneously.' 



So far as can be judged by the scanty palaeontological evidence, 

 the Gopeng Beds are where we might expect to find glacial beds 

 in the succession; but they naturally differ very considerably from 

 the other boulder-beds in petrological composition, because the ice 

 that was instrumental in their formation passed over stanniferous 

 rocks rich in the minerals that constitute the usual satellites of 

 cassiterite : namely, tourmaline, topaz, and kaolin. 



